IL13 and seminoma: We identified all proteins secreted by seminoma (TCam‐2), EC (2102EP and NCCIT), choriocarcinoma (JAR and JEG‐3), and yolk‐sac tumor cell lines (GCT72) as well as fibroblasts (MPAF and HVHF2), endothelial cells (HUVEC), MIL4/IL13 macrophages (THP‐1‐ MIL4/IL13) and T‐lymphocytes (JURKAT) (Figs S1F–H, S2 and S3; Table S3M–U).